The present invention provides a novel influenza virus wherein both the NS and the PB1 gene segments are modified and wherein the PB1-F2 ORF is modified by introduction of at least one stop codon. According to a specific embodiment, the influenza virus is lacking functional NS1 and PB1-F2 proteins and is replication deficient in interferon competent cells.
Additionally, a vaccine formulation comprising said modified influenza virus is provided and its use for prevention of influenza infection.